An active layer is an important role in a transistor. A metal oxide semiconductor transistor includes a metal oxide semiconductor layer as the active layer. Comparative to an amorphous-silicon thin film transistor including an amorphous-silicon layer as the active layer, the metal oxide semiconductor transistor has higher carrier mobility. Comparative to a low temperature poly-silicon thin film transistor including a low temperature poly-silicon layer as the active layer, the metal oxide semiconductor transistor has a simpler manufacturing process. In addition, the metal oxide semiconductor layer has a better uniformity than the amorphous-silicon layer or the low temperature poly-silicon layer so that the metal oxide semiconductor transistors has a better performance than the amorphous-silicon thin film transistors or the low temperature poly-silicon thin film transistors.
Currently, in order to further improve the performance of the transistor, one method is to increase the carrier mobility of the transistor. Typically, the active layer of the transistor is commonly formed to a polycrystalline structure so as to improve the carrier mobility of the transistor. For example, a poly-silicon transistor utilizing a poly-silicon layer as the active layer has higher carrier mobility. However, the manufacturing process of the poly-silicon transistor is more difficult, and the poor uniformity of forming the poly-silicon layer will affect the performance of the transistor. In addition, in order to further improve the performance of the transistor, another method is to change a material composition of the active layer. However, it is difficult to develop a new material, which is not benefit for speeding up the performance improvement of the transistor.